Hydrocracking of hydrocarbon feedstocks is often used to convert lower value hydrocarbon fractions into higher value products, such as conversion of vacuum gas oil (VGO) feedstocks to various fuels and lubricants. Typical hydrocracking reaction schemes can include an initial hydrotreatment step, a hydrocracking step, and a post hydrotreatment step, such as dewaxing or hydrofinishing. After these steps, the effluent can be fractionated to separate out a desired diesel fuel and/or lubricant oil base oil.
A process train for hydrocracking a feedstock can be designed to emphasize the production of fuels or the production of lubricant base oils. During fuels hydrocracking, typically the goal of the hydrocracking is to cause conversion of higher boiling point molecules to molecules boiling in a desired range, such as the diesel boiling range, kerosene boiling range, and/or naphtha boiling range. Many types of fuels hydrocracking processes also generate a bottoms component from hydrocracking that potentially can be used as a lubricant base oil. However, the lubricant base oil is produced in a lesser amount, and often is recycled and/or hydrocracked again to increase the fuels yield. In hydrocracking for forming a lubricant base oil the goal of the hydrocracking is typically to remove contaminants and/or provide viscosity index uplift for the feed. This results in some feed conversion, however, so that a hydrocracking process for generating a lubricant base oil typically produces a lesser amount of fractions that boil in the diesel boiling range, kerosene boiling range, and/or naphtha boiling range. Due to the difference in the desired goals, the overall process conditions during fuels hydrocracking of a given feedstock typically differ from the overall process conditions during hydrocracking for lubricant base oil production on a similar type of feedstock.
U.S. Pat. No. 7,261,805 describes a method for dewaxing and cracking of hydrocarbon streams. A feedstock with an end boiling point exceeding 650° F. (343° C.) is contacted with a hydrocracking catalyst and an isomerization dewaxing catalyst to produce an upgraded product with a reduced wax content. The feedstock is described as contacting the hydrocracking catalyst first, but it is noted that the order of the steps can be changed without a significant decrease in yield.
U.S. Pat. No. 6,103,101 describes a method for hydroprocessing of a feedstock for either lubricant base oil production or for fuels production. The hydroprocessing includes sequentially contacting a feed with a demetallization catalyst, a hydrotreating catalyst that includes Group VIB and Group VIII base metals, a hydroisomerization/hydrocracking catalyst that includes Group VIB and/or Group VIII metals, and a hydrofinishing catalyst that includes Group VIB and Group VIII base metals. In one configuration described as being suitable for fuels production, the bottoms product from fractionation of the hydroprocessed effluent can be recycled to the beginning of the hydroprocessing sequence.
U.S. Patent Application Publication 2012/0248008 describes a method for fuels hydrocracking with dewaxing of fuel products. In a first stage, a feed is hydrotreated and/or hydrocracked, with the resulting effluent being exposed to a dewaxing catalyst. The dewaxing catalyst can be a ZSM-48 catalyst with supported Pt as a hydrogenation metal. The hydrotreated/hydrocracked and dewaxed effluent can then be fractionated to form fuel product streams. A bottoms portion from the fractionator can be passed into a second hydrotreating and/or hydrocracking stage for further conversion of the feed.